Add Nicholas and Matt, Remove Seth for group::orchestration and group::health

Replace @sengelhard with @nicholasklick and @mnohr in the triage packages for ~"group::orchestration" and ~"group::health" respectively.

Consider adding documentation to the handbook pages for Triage Operations when creating a new triage policy or triage package:

• https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/source/handbook/engineering/quality/triage-operations/index.html.md